Photoconductography employing organic onium cation



March 9, 1965 v. TULAGIN ETAL 3,172,826

PHOTOCONDUCTOGRAPHY EMPLOYING ORGANIC ONIUM cAnou Filed April 18, 1960 l0 I8 aaaaaaaaa I2 34 I aaaaa 22 \g j V uvmvrons VSEVOLOD TULAGIN ROBERT F. COLES RICHARD A. MILLER 5 mhm ATTORNY United States Patent M 3,172,826 PHOTOCONDUCTOGRAPHY EMPLOYING ORGANIC ONIUM CATION Vsevolod Tulagin, St. Paul, Robert F. Coles, North St.

Paul, and Richard A. Miller, St. Paul, Minn, assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Apr. 18, 1960, Ser. No. 22,931 8 Claims. (Cl. 20418) This invention relates to new and useful permanent reproductions and their method of preparation by selectively depositing and irreversibly bonding a water insoluble organic compound on the surface of a photoconductor.

A method for making visible reproductions electrolytically is described in the application of Johnson and Neher, Ser. No. 575,070, filed March 30, 1956, now US. 3,010,883. The Johnson and Neher application also discloses the preparation of light sensitive sheet material from a conductive backing and a photoconductor which is also useful in the practice of this invention.

An object of this invention is to disclose a method for selectively depositing water insoluble organic compounds on the surface of a photoconductor, thereby producing reproductions in a fast and efficient manner.

Another object of this invention is to disclose a process for preparing colored reproductions by electrophotography. These colored reproductions are prepared by successively applying subtractive primary colors to the surface of the photoconductor. The methods of making colored reproductions from subtractive primaries is described in J. S. Friedmans A History of Color Photography, American Photographic Publishing Company, Boston, Mass. (1944).

It has now been discovered that permanent reproductions may be made on the surface of a dye-sensitized photoconductor uniformly bonded to an electrically conductive carrier by selectively depositing and irreversibly bonding a Water insoluble'organic compound to the surface of the photoconductor by electrolytic decomposition of onium ions. The photoconductor surface is exposed to a light source in selected areas to render the photoconductor conductive in the exposed areas. The photoconductor surface is then contacted with a water solution containing an onium ion. When an electrical current is passed through the water solution, the positively charged onium ion is attracted to the conductive areas of the cathode-photoconductor and is electrolytically de composed to deposit a water insoluble substance on the exposed surface of the photoconductor.

The term dye-sensitized indicates that the photoconductor has been treated with an organic dyestutf so that radiant energy is absorbed by the dye on the surface of the photoconductor and the energy is transferredto the photoconductor thereby making the photoconductor conductive.

This process may be employed in various ways to prepare permanent reproductions. The preferred method is to deposit a colored water insoluble compound and in this manner the photoconductor is colored directly. If the water insoluble substance is colorless it may be colored in a subsequent step to produce a negative image or it may serve as a protective coating-for the portions of photoconductor covered and the unprotected areas are then colored or modified chemically in some other manner, such as by dyeing or etching away the photoconductor with an acid or solvent; Likewise, the surface wetting characteristics of selected areas of the photo- 3,172,825, Patented Mar. 9, 1965 conductive sheet can be modified to attract or repel water or oil. This latter method is particularly suitable for the production of lithographic plates where the photoconductor is rendered hydrophobic by the water insoluble organic compound. The water insoluble compound may also be derived from an emulsifying agent which upon decomposition releases dispersed water insoluble pigments which are then deposited on the selected areas of the photoconductor.

The chemical decomposition effected electrolytically in the practice of this invention relates to onium compounds because they impart water solubility to many water insoluble compounds and because they are positively charged compounds. The term onium compounds encompasses quaternary nitrogen compounds, sulfonium, phosphonium, arsonium, oxonium and similar compounds that have a positively charged electronegative atom. The decomposition products of these compounds which are deposited on the photoconductor surface are water insoluble compounds, even in the presence of an acid or base.

In the drawings:

FIGURE 1 is a perspective view of developing apparatus useful in the practice of this invention and FIGURE 2 is a cross-sectional view of FIGURE 1 along section line 22.

Developer tray 19 is composed of a base plate 12, which also serves as an eloctrode, top clamping frame member 14, and an intermedate open frame member 16 forming upstanding walls around the base plate periphery. Frame member 14 and base plate 12 have cooperating, releasable clamping means 18, which draw these members toward one another when engaged to render the tray 10 water tight.

The open frame member 1:: is composed of a non-conductor such as polyethylene, polytetrafluoroethylene or polytrifiuorochloroethylene and is provided with a ledge 20 for supporting electrode 22 such that an electrical current passing to electrode 22 from the base plateelectrode 12 passes through a photoconductor sheet 24 which is interposed between the open frame member 16 and the base plate 12. This photoconductor sheet 24 is composed of an electrically conductive carrier 26 which is placed in intimate contact with the base plate 12 and photoconductor particles 28.

In order to selectively deposit images 30 on the photo conductor sheet 24;, a solution 32 is placed in the developer tray 10, electrode 22 is connected to the positive terminal of the direct current power source 34' and'the base plate 12 is attached to the negative terminal of the power supply 34. When arranged in this manner the electrical current passes through solution 32 and the photoconductivc areas of the photoconductive sheet 24 resulting in image deposits 36* on the cathode-photoconductive surface. In order to graphically show the photo conductor particles 23 and the image deposit 30, they have been represented in FIGURE 2 in exaggerated size.

A preferred procedure for producing an image in accordance with the teachings of this invention is as follows:

(1) .The negative electrode from a direct current power supply 34 is attachedto the metal base plate thereby making electrical contact with the conductive backing of the photoconductor sheet 24. (2) The photoconductor sheet 24 in the developing tray 10 is exposed to light in selected areas such as by focusing and projecting a photographic negative on the photoconductor sheet 24 through a projector. (3). The electrode 22 is placed on the ledge 26 and connected to the positive terminal of the direct current power supply/34. (4). The solution 32 is added to the tray. (5) The electrical current is turned on so as to effect the electrolytic development. (6) The solution is poured oil and the photoconductor sheet is thoroughly washed with water. After suitable dark adaptation additional images may be put on the photoconductor sheet by repeating the above procedure. An especially useful method for dark adaptation of the photoconductor sheet is to placeit in contact with water heated to at least 100 F. whichmay be accomplished simultaneously with the washing by employing the hot water as the Wash water.

Color reproductions may be obtained by carrying out the above procedure three times with monochromatic light. For example, a color negative is placed in a projector equipped with a photofiood lamp and a red filter is interposed between the photofiood lamp and the photoconductor sheet, preferably between the color negative and the photoflood lamp thereby exposing the photoconductor sheet selectively to red light. A cyan image is then developed on the photoconductor using a cyan dye. The photoconductive paper is then washed with warm water (heated to at least 100 F.) and dried with a stream of air. The developing tray is then returned to the enlarger and a green filter is interposed between the light source and the photoconductor sheet. After the photoconductor has been exposed selectively to the green light, the above process is repeated using a magenta dye. This procedure is repeated again to produce a yellow image on those areas selectively exposed through a blue filter. In this manner a full true-to-life color picture is obtained by electrophotography.

Generally speaking, the light intensity of the projected image, time of exposure which may be from 0.1 second to sixty seconds, and period of electrolytic development which may be from 1 to 36 seconds at a voltage of from 5 to 150 volts are varied in accordance with the quality of the image required or desired and the relative effectiveness of the photoconductor surface.

PREPARATION OF PHOTOCONDUCTOR SHEET (A) A Waring Blendor mixer is employed to thoroughly blend the following ingredients over a period of minutes:

Methyl-isobutyl ketone 139 Zinc oxide (USP 12) having a particle size of less than 40 microns 252 Binder toluene solution of butadiene (30 parts by weight) and styrene (70 parts by weight) copolymer] 210 sensitizing dyes are then added to the blend as 0.5% methanol solutions in order to dye-sensitize the photoconductor sheet as follows:

More

(lg fgplor index, 2d ed., Chorley & Pickersgill Ltd, Leeds After being blended for an additional five minutes and filtered through a coarse sintered glass filter, the blend is coated with a doctor blade coater onto an aluminum sheet (3 mil) to a wet thickness of .006 inch.

When dry and fully dark adapted, this sheet is used to produce reproductions and had high response spectral bands at 460465 mu, 5 60 mu and 660 mu.

(B) Zinc oxide, USP 12 (34.4 parts by weight); a binder (29.6 parts by weight), Pliolite E-7, a product of the Goodyear Tire and Rubber Company, Akron, Ohio; and acetone (11.8 parts by weight) were mixed in a ball mill for 8 hours until a smooth dispersion was obtained. This dispersion, diluted with ethyl acetate (23 parts by weight), was mixed with 0.5% methanol dye-sensitizer solutions of Phosphine R (2 parts), a product of the General Dyestutf Corporation, and Xylene Cyanol FF (0.6 part), a product of British Drug Houses Ltd. The resulting mixture was filtered through a 325 mesh screen and coated at a wet thickness of .007" on a 3 mil aluminum backing. After being dried in a stream of warm dry air and dark adapted by storage in the absence of light for 24 hours, the resulting photoconductor sheet could be used to prepare reproductions in accordance with the teachings of this invention.

Because of their flexibility, durability, and resistance to crease formation, photoconductor sheet backings prepared by vapor deposition of a metal, such as aluminum, on a paper or plastic backing are especially useful. Polyethylene terephthalate films (5 mil) are preferred.

The procedure employed in the following examples to prepare reproductions by the electrolytic decomposition of onium compounds on the surface of a zinc oxide photoconductor sheet prepared as described above was as follows:

(1) The negative electrode from a direct current power supply was attached to the metal base of a developer tray as illustrated in FIGURES l and 2 of the drawing thereby making electrical contact with the aluminum backing of the photoconductor sheet.

(2) The photoconductor sheet retained in the developer tray was exposed to a light source in the selected areas by projecting an image on the photoconductor sheet with the projector having a low 1'' stop projection range and a 500 watt tungsten projection lamp as the light source, thereby rendering select areas conductive. Relative humidity of the atmosphere in the work area should be less than 40 percent.

(3) An electrode attached to the positive terminal was placed in the developer tray and the desired solution was added to the tray.

(4) After a total lapse of time of about 20 seconds after exposure, a 30 volt electrical current was then passed through the photoconductor at the conductive areas for a period of 10 seconds.

(5) The solution was removed from the developer tray and the photoconductor sheet was thoroughly washed with water heated to about F.

(6) If the photoconductor sheet was to be re-exposed, it was placed in contact with the warm Water heated to 140 F. for a period of at least 20 seconds to restore it to a dark adapted state and the sheet was then dried by placing it under a stream of air.

Example 1 This example shows the preparation of chromogenic onium ions and the electrotlytic decomposition of the onium ions to directly form a colored image on a zinc oxide photoconductor sheet prepared as described above.

(A) CYAN DYE DEPOSITION Alcian Blue 8' GN (5 g.) which is described in The Chemistry of Synthetic Dyes, by K. Venkataraman, Academic Press, Inc., New York, New York (1952), dissolved in water (100 ml.) was deposited on the exposed areas following the procedure outlined above. The excess dye was removed by washing tie photoconductor with water. A firmly attached and completely insoluble cyan image resulted on the surface of the photoconductor in those areas that had been rendered conductive by exposure. It was further observed that the unexposed portions of the photoconductor were substantially free of color and that the density of the dye image on the exposed areas was inversely proportional of the density of the negative.

(B) YELLOW DYE PREPARATION AND DEPOSITION (l) A yellow thiuronium compound was prepared by adding bis(chloromethyl)-4,4-bis(6 methylbenzthiazyl- 2)azobenzene (5 g.) to N,N,N',N-tetramethylthiourea (25 g.) and enough water to make a thick paste. This paste was heated to 90 C. and stirred for a period of one and one-half hours as disclosed in British Patent No. 576,270. The resulting solution was poured into acetone (200 g.) and the resulting yellow precipitate was filtered and washed with acetone and dried.

A 0.5% solution of the yellow precipitate in water was used to selectively deposit a yellow dye on a zinc oxide photoconductor sheet in those areas that had been rendered photoconductive by exposure to light by the procedure described above.

(2) An azcic pigment (5 g.) prepared by coupling Naphtol ASLG and Fast Red Salt FRN was dissolved in 100% sulfuric acid (75 g.) at C. and chloromethyl methyl ether (25 g.) was added. The mixture was then stirred and rapidly heated to 60 C. and maintained at this temperature for 25 minutes at the end of which time the mixture was poured on ice. The resulting solid was removed by filtration, washed with cool water, and dried. T he chloromethylated compound g.) was then mixed with N,N,N,N'-tetrarnethylthiourea g.) and sufiicient water to make a thick paste. This mixture was heated and stirred at 90 C. for about one and one-half hours. The solution was then mixed with acetone (200 g.) and the resulting dark precipitate was separated fro-m the liquid portion by decantation. The solid was then washed with acetone, filtered and dried.

A 5% aqueous solution of the solid was employed to prepare a negative yellow print on the zinc oxide photoconductor sheet in accordance with the procedure outlined above.

(3) Indigo Yellow (2.5 g.) was added to a cooled mixture of 100% sulfuric acid (40 ml.) and bis('chloromethyl) ether (5 rnl.). The temperature was raised to 60 C. and held for 15 minutes. After pouring onto ice, the resulting solid was collected; washed with water and heptane. The damp filter cake was added to molten N,N,N',N'-tetramethylthiourea (5 g.) and heated on a steam bath for one-half hour. The reaction mixture was poured into a large volume of acetone and the resulting gum collected. This dissolved readily in water to give a yellow-brown solution which produced a negative yellow image on a zinc oxide photoconductor sheet in accordance with the procedure described above. A heavy, loosely attached dye layer precipitated imagewise on the conductive areas. This layer was Washed ofi" to expose a more substantive yellow sublayer.

(4) Ethyl benzoylacetate was condensed in boiling xylene with 2,5-dimethoxyaniline to produce the benzoylacetanilide which was coupled in a pyridine solution Withthe diazo from the amine obtained by condensing p-acetylaminobenz/enesulfonyl chloride with N,N-diethylethylened'iamine followed by hydrolysis of the acetyl group in aqueous hydrochloric acid.

(a) The yellow azo dye (2.9 g., 0.005 mole) was heated'with phenacylbromide (2 g., 0.01 mole) and sodium bicarbonate (0.5 g., 0.005 mole) in ethanol (50 ml.-) for 20 hours on a steam bath. The insoluble salt was removed by filtration and the filtrate cooled. A yellow solidwas collected from the filtrate and dried. The yellow solid was dissolved in water to make a 0.5% solution and this solution was used to obtain a brilliant negativeyellow dye image with a strong metallic lustre on the surface of a zinc oxide photoconductor sheet by electrolytic decomposition of the quaternary group on the conductive areas of the sheet.

(15) The yellow azo dye (3 g.) was dissolved in hot glacial acetic acid (25' ml.) on a steam bath and his (chloromethyl) ether (2 ml.) added. The heating was discontinued and the solution stirred for one hour. The solvent was removed at'reduced pressure and the residual gum dissolved in benzene. The chloromethyl compound was isolated by precipitation with heptane to yield a gum which solidified on trituration with fresh heptane. The solid was collected, washed with heptane and vacuum dried.

The chloromethyl compound was then added to molten N,N,N,N'-tetrarnethylthiourea (10 g.) heated on a steam bath. The mixture was heated for one hour and the clearmelt poured into boiling heptane (200 ml.). After decanting the hot solvent, the gum we re-extracted with fresh heptane and cooled to yield a solid which was collected and dried. A 1% solution of this solid in water was used to obtain a negative yellow image of bronze lustre on a zinc oxide photoconductor sheet by the above described process.

(C) MAGENTA DYE PREPARATION AND DEPOSITION (1) Preparation of the thiuronium salt of a derivative 0 Basolan Chrome Brilliant Red 3BM.

Fifteen grams of the above dyestufl were added to thionyl chloride (40 ml). One drop of pyridine was added and the mixture allowed to stand overnight. The excess thio-nyl chloride was'removed at reduced pressure and the residue was extracted with dry benzene.

p Nitr'o-aniline (5.5 g'.,- 0.04' mole) in 30 ml. dry dimethylformamide was added slowly while stirring to the above carbo'nyl'chlo-ride (1112 g, 0:02 mole); Pyridine (5' ml.) was added d'rop wise and the reaction mixture heated'on a' steambathfor one-half hour. The solution Was'poured into water. The resulting solid was separated by filtration and extracted with'sodium bicarbonate and then dilute hydrochloric acid;

This filter cake was'dissolved in 75% aqueous pyridine ml.). Several drops of hydrochloric acid were added and powdered iron (15 g'.) was added slowly td the hot solution. After heating for one hour and filtering hot, the filtrate was diluted to one liter with water. The resulting solid was collected by filtration and then redissolved in glacial acetic acid (75 nil). This solution was filtered to remove residual insolubles and the filtrate was poured into water (200 mi The solid product was collected, washed with water and methanol, and dried. This solid product (3 g.) was added to ml. chloro' acetyl chloride. The resulting warm solution was treated with anhydrous potassium acetate (2 g.). Excess chloroacetyl chloride was removed at reduced pressure and the residue treated with ice and water. The resulting gum was triturated with dilute bicarbonate solution to yield a red-brown solid which was collected by filtration and washed with water.

The red-brown solid was added to molten N,N,N,N'- tetramethylthiourea g.) and the melt heated for onehalf hour on a steam bath. The resulting deep red solution was poured into acetone (400 ml.) to yield a reddish gum which was solidified by repeated trituration with fresh acetone. A 1% aqueous solution of the solidifled product deposited a positive magenta image on zinc oxide photoconductor sheet as described above. The addition of a small amount of acetic acid to the solution resulted in production of a negative magenta image on the photoconductor using the same process.

(2) T hiuronium salt of Anihragen Red Violet RHC. The dyestuff, Anthragen Red Violet RHC, a product of General Aniline Corp., was freed from dyeing assistants by extraction with water and acetone. Five grams of this purified material were added with stirring at below 10 C. to 100% sulfuric acid (75 g.) and bis(chloromethyl) ether (25 g.). The temperature was raised to 60 C. and held for minutes. The mixture after cooling was poured onto ice and water to produce a purple powder which was collected by filtration, washed with water and dried.

The purple powder was added to molten N,N,N,N'- tetramethylthiourea (20 g.). After heating the melt on a steam bath for 20 minutes it was poured into acetone (500 ml.) and the resulting solid collected and dried. This material was dissolved in water to make a 1% solution, and filtered. The solution was then selectively deposited as a reddish purple negative image on the zinc oxide photoconductor as described above.

(3) Thiurom'um salt of a Naphtol AS azo dye.--

p-Aminoacetanilide was reacted with Z-hydroxy-S- naphthoic acid in hot toluene with the aid of phosphorus trichloride. The acetyl group was then hydrolyzed by warming with dilute aqueous alcoholic potassium hydroxide for several hours. The product was coupled in pyridine and dimethylformamide solution with the diazo from 2-methyl-4-chloroani1ine. The resulting azo dye was chloroacetylated with excess chloroacetyl chloride in hot toluene. The resulting reaction product was reacted with N,N,N',N'-tetrarnethylthiourea by adding the dye to a melt of the tetramethylthiourea at 150 C. and stirring for four minutes. The melt was cooled, digested with water and the solution recooled. The precipitated tetramethylthiourea was removed by filtration and the magenta colored solution of the thiuronium salt, the structure of which is shown above, was used to obtain a negative image on zinc oxide by the above-described method.

Example 2 This example demonstrates various applications of this invention made possible by the decomposition of water soluble, colorless onium ions and the deposition of a colorless image of a water insoluble decomposition product.

A solution of tetradecylarnine (8.5 g.) and potassium acetate (39 g.) in methanol (50 ml.) was added over a period of 15 minutes to a solution of p-chloromethylbenzenesulfonyl chloride (10 g.) dissolved in ml. of methanol. The mixture was stirred for two hours and the white precipitate which formed was removed by filtration. The precipitate was washed with water and recrystallized from methanol to produce N-tetradecyhpchloromethylbenzenesulfonamide (6 g.).

N-tetradecyl p chloromethylbenzenesulfonamide (1.0 g.) and N,N,N,N-tetramethylthiourea (0.4 g.) were mixed and heated at 110 C. for several minutes. Heptane was added, the mixture was heated, stirred and centrifuged. The gelatinous solid (1.2 g.) was then washed with petroleum ether and dried.

A solution of this thiuronium salt in water was employed to deposit a colorless negative image on a zinc oxide photoconductor sheet in areas rendered conductive in accordance with the above outlined procedure. The areas of the sheet so coated were water repellent and were preferentially dyed to produce a colored negative image with an aqueous solution of Basolan Chrome Brilliant Red BBM, a product of Badische Anilinund Sodafabrik AG., Ludwigshafen, Germany. The unexposed areas which were not coated by the colorless image were treated as follows: (1) A dilute solution of hydrochloric acid and acetic acid was employed to remove the zinc oxide from these unprotected areas. The zinc oxide areas covered by the deposited compound were not aifected. (2) The unexposed areas of the zinc oxide photoconductor sheet were preferentially dyed with an acid soluble azo dye solution and a positive dye image was formed in this manner after washing off the excess dye. (3) A borax solution was employed to render the unexposed portions of photoconductor sheet hydrophilic, the coated portions already being hydrophobic. The sheet was then treated with printers ink in the same manner that litho graphic plates are treated with printers ink and the exposed portions which are hydrophobic were ink receptive.

Example 3 This example shows the deposition of pigments and dyes dispersed in a solution containing onium ions.

(A) A solution of the thiuronium salt prepared as described in Example 2 containing a suspended pigment derived from Naphtol AS-LG and Fast Red Salt ITRN was decomposed electrolytically to prepare a yellow colored negative image on the exposed areas of the photoconductor sheet using the procedure outlined above.

A black image was obtained when the suspension contained carbon black.

(B) To m1. of a 0.5% aqueous solution of p (N tetradecyl)carbamylphenyltrimethylammonium chloride, prepared by reacting p-carbomethoxyphenyltrimethylammonium chloride (7 g.) and tetradecyl amine (7 g.) was added 3 ml. of an acetone solution containing 100 mg. of the yellow dye:

( zHbh a The resulting dispersion was used as the electrolyte for the electrolytic development of an image on the exposed areas of a zinc oxide photoconductor sheet using the procedure outlined above. After washing, a clean bright yellow negative image was obtained.

(C) A solution of 50 mg. of the dye i 1 TH HgCH2N(OzHa)2 and l g. Beetle Resin 227-8, a product of the American Cyanamide Company, in ml. of alcohol was added to 100 ml. of .5% aqueous solution of p-(N-tetradecyl) carbamylphenyltrimethylammonium chloride. When the resulting dispersion was used as the electrolyte for the development of an exposed zinc oxide photoconductor sheet in the manner outlined above, a purple black negative image of good density and gradation was obtained.

(D) A mixture of cetyldimethylamine (13 g.) and phenacyl bromide (10 g.) in 60 ml. of dry benzene was allowed to stand at room temperature for 72 hours. The benzene was removed by distillation at reduced pressure and the residue was crystallized from acetone.

A solution of the resulting cetyldimethylphenacylammonium chloride (.6 g.) zein (.5 g.) and Azosol Fast Yellow GT, a product of the General Dyestutf Corporation, in hot alcohol (10 ml.) was added to 106 ml. of water with rapid agitation. This dispersion was used as an electrolyte in the process of this invention as described above and gave bright yellow images of excellent adhesion and gradation.

This yellow solution was used as the third image to make full color images on the zinc oxide photoconductor sheet in three stages wherein the first image was Alcian lue 8 GN as described in Example 1, and the second image was Astraphloxine FF.

A solution of cetyldimethylphenacylammonium chlo ride (.6 g.), Azosol Fast Red 3 BA, a product of the General Dyestuil Corporation (.2 g.), and zein (.2 g.) in hot alcohol (10 ml.) was added to 100 ml. of water with rapid agitation. The suspension so obtained was used to produce magenta images on zinc oxide photoconductor sheets as outlined above.

(E) Cyanuric chloride was reacted with one equivalent of N -tetradecylsulfanilamide in cold acetone in the presence of sodium bicarbonate. The solid was collected, washed with Water and dried. A sample of the product was added to five parts of molten N,N,N,N'- tetramethylthiourea on a steam bath and heated for onehalf hour. The melt was diluted with water, cooled and the excess tetramethylthiourea removed by filtration.

A colorless oily negativeimag'e was selectively deposited from the'filtrate on the conductive surface of a photoconductor by decomposition of the solubilizing grouping. If a fine suspension of a pigment, such as india ink, is added to the solution of the thiouronium salt, a negative dye image is obtainedsince a carbon image is deposited along with the oily deposit.

(F) A solution of p-chlorome-thylbenzoyl chloride (18.5 g., 0.1 mole), prepared by the procedure described in I.A.C.S. 65 2282 (1943), in hot xylene (150 ml.) was added to 1,5-diaminoanthraquinone (6 g., 0.023 mole). The mixture was heated at reflux and after one-half hour a second portion of the 1,5-diaminoanthraquinone (6 g.) was added. After three hours heating, the evolution of hydrogen chloride ceased and the reaction mixture was cooled. A yellow solid (MP. 22424() C.) was recrys tallized from fresh xylene. This yellow solid was then added to ten times its weight of molten N,N,N',N'- tetramethylthiourea heated on a steam bath. After heating for five minutes, the not melt was extracted with boiling heptane. The thiouronium salt remaining insoluble in heptane is soluble in water, and aqueous solutions of it produce yellow negative images on zinc oxide photoconductors as described above.

Example 4 A sheet of zinc oxide electrophotographic paper was exposed in all areas to white light, and then colored with Alcian Blue 8 GN by electrolytic deposition on the surface of a zinc oxide photoconductor sheet to produce a blue-green sheet. This sheet was dark state adapted by contacting it' with hot water followed by drying. The sheet was then exposed "to a photographic image, contacted with a suspension of titanium dioxide in a dilute aqueous solution of the th'iuroniur'n salt from N-tetradecyl-p-chloromethylbenzenesulfonamide and N,N,N,N'- tetramethylthiourea. Concurrently with the decomposition of the thiouronium salt, the titanium dioxide was selectively deposited in the light-struck areas of the sheet. The remaining blue-green areas then gave the appearance of a positive image.

The method of this example is useful in producing a full color positive picture by employing a photoconductor sheet which is colored by a mosaic pattern of yellow, cyan, and magenta sites, wherein the cyan sites are sensitized to red light, the magenta sites are sensitized to green light, and the yellow sites are sensitized to blue light. In this way, the titanium dioxide or other white opaque pigment is selectively deposited on the exposed sites and the remaining sites not obscured by the titanium dioxide represent the color of the exposing light in that area.

We claim:

1. A method for selectively depositing and irreversibly bonding a water insoluble substance on the surface of a dye-sensitized photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a light source in the selected areas thereby rendering the exposed areas electrically conductive, contacting the conductive areas with a Water solution containing a water soluble organic onium cation which decomposes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductorcathode thereby attracting said cation to the conductive areas of the photoconductor and electrolyticall decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor.

2. A method for selectively depositing and irreversibly bonding a colored water insoluble substance on the surface of a dye-sensitized photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a light source in'the selected areas thereby rendering the exposed areas electrically conductive, contacting the conductiveareas with a water solution containing a water soluble organic oniurn cation which decomposes electrolytically to form a colored water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductor-cathode thereby attracting said cation to the conductive areas of the photoconductor and electrolytically decomposing said cation to produce a colored Water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor.

3. A method for selectively depositing and irreversibly bonding a water insoluble substance on the surface of a dye-sensitized photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a light source in the selected areas thereby rendering the exposed areas electrically conductive, contacting the conductive areas with a water solution containing a water soluble organic onium cation which de- 1 1 composes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the pbotoconductorcathode thereby attracting said cation to the conductive areas of the photoconductor, electrolytically decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconduc'tor, and coloring the water insoluble compound deposit with a colored substance. 7

4. A method for selectively depositing and irreversibly bonding a water insoluble substance on the surface of a dye-sensitized photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a light source in the selected areas thereby rendering the exposed areas electrically conductive, contacting the conductive areas with a water solution containing a water soluble organic onium cation which decomposes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductorcathode thereby attracting said cation to the conductive areas of the photoconductor, electrolytically decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor, and coloring the areas of the photoconductor not covered by said water insoluble compound with a colored substance.

5. A method for selectively depositing and irreversibly bonding a water insoluble substance on the surface of a dye-sensitized photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a light source in the selected areas thereby rendering the exposed areas electrically conductive, contacting the conductive areas with a water solution containing a water soluble organic onium cation which decomposes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductorcathode thereby attracting said cation to the conductive areas of the photoconductor, electrolytically decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor, and etching away the areas of the photoconductor not covered by said water insoluble compound.

6. A method for selectively depositing and irreversibly bonding a water insoluble substance on the surface of a hydrophilic dye-sensitized photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a light source in the selected areas thereby rendering the exposed areas electrically conductive, contacting the conductive areas with a water solution containing a water soluble organic onium cation which decomposes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductor-cathode thereby attracting said cation to the conductive areas of the photoconductor and electrolytically decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor, thereby rendering the selected areas hydrophobic.

7. A method for selectively depositing a water insoluble substance on the surface of a dye-sensitized photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a light source in the selected areas thereby rendering the exposed areas electrically conductive, contacting the conductive areas with an aqueous dispersion containing a water soluble organic onium cation which decomposes electrolytically to form a Water insoluble compound, passing an electrical current through the aqueous dispersion and the conductive areas of the photoconductor-cathode thereby attracting said cation to the conductive areas of the photoconductor and electrolytically decomposing said cation to destroy the dispersion and deposit the dispersed particles on the exposed areas of the photoconductor.

8. A method for preparing a multi-colored reproduction by selectively depositing and irreversibly bonding water insoluble organic substances on the surface of a photoconductor bonded to an electrically conductive carrier which comprises exposing said photoconductor to a monochromatic image from a light-image of a colored subject, contacting the conductive areas with a water solution containing a water soluble organic onium cation which decomposes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductor-cathode thereby attracting said cation to the conductive areas of the photocondnctor, electrolytically decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor, desensitizing the photoconductor to remove any latent image and to restore the photoconductor to its dark adapted state, exposing said photoconductor to a second monochromatic image from a light-image of said colored subject, contacting the conductive areas with a water solution containing a second water soluble organic onium cation which decomposes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductor-cathode thereby attracting said cation to the conductive areas of the photoconductor, electrolytically decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor, desensitizing the photoconductor to remove any latent image and to restore the photoconductor to its dark adapted state, exposing said photoconductor to the third monochromatic image from a light-image of said colored subject, contacting the conductive areas with a water solution containing a third water soluble organic onium cation which decomposes electrolytically to form a water insoluble compound, passing an electrical current through the water solution and the conductive areas of the photoconductor-cathode thereby attracting said cation to the conductive areas of the photoconductor, and electrolytically decomposing said cation to produce a water insoluble organic compound which is deposited and irreversibly bonded on the exposed areas of the photoconductor.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Schmidt: Organic Chemistry, Oliver and Boyd, London, 7th ed., 1955, pages 478-482.

Grieg: Proceedings of the I.R.E., October 1948, pp. 1224-1235, 

1. A METHOD FOR SELECTIVELY DEPOSITING AND IRREVERSIBLY BONDING A WATER INSOLUBLE SUBSTANCE ON THE SURFACE OF A DYE-SENSITIZED PHOTOCONDUCTOR BONDED TO AN ELECTRICALLY CONDUCTIVE CARRIER WHICH COMPRISES EXPOSING SAID PHOTOCONDUCTOR TO A LIGHT SOURCE IN THE SELECTED AREAS THEREBY RENDERING THE EXPOSED AREAS ELECTRICALLY CONDUCTIVE, CONTACTING THE CONDUCTIVE AREAS WITH A WATER SOLUTION CONTAINING A WATER SOLUBLE ORGANIC ONIUM CATION WHICH DECOMPOSES ELECTROLYTICALLY TO FORM A WATER INSOLUBLE COMPOUND, PASSING AN ELECTRICAL CURRENT THROUGH THE WATER SOLUTION AND THE CONDUCTIVE AREAS OF THE PHOTOCONDUCTORCATHODE THEREBY ATTRACTING SAID CATION TO THE CONDUCTIVE AREAS OF THE PHOTOCONDUCTOR AND ELECTROLYTICALLY DECOMPOSING SAID CATION TO PRODUCE A WATER INSOLUBLE ORGANIC COMPOUND WHICH IS DEPOSITED AND IRREVERSIBLY BONDED ON THE EXPOSED AREAS OF THE PHOTOCONDUCTOR. 